1. Field of the Invention
The present invention relates to a parking lock for a vehicle having an electrical device, and to a method for operating such a parking lock. The present invention also relates to an electrical drive for a vehicle.
2. Description of the Related Art
Motor vehicles such as passenger vehicles have a parking brake for preventing the vehicle from rolling away inadvertently when the vehicle is parked. A problem with known parking brakes in terms of safety is that in some cases the parking brake cannot completely prevent the vehicle from rolling away inadvertently, particularly when said vehicle is located on a grade.
For this reason, it is desirable to use a parking lock in addition to the parking brake. The parking lock is intended to make it impossible for the vehicle to roll away inadvertently at any time and in any place. In particular, the parking lock is designed to prevent the vehicle from rolling away when the vehicle is parked on a grade.
When the vehicle includes a conventional internal combustion engines with a manual transmission, the additional parking lock may be provided by also selecting a low gear, for example the reverse gear or the like, in addition to operating the actual parking brake. In this solution, the compression forces and friction forces in the internal combustion engine produce a braking effect which supplements the braking force of the parking brake.
However, when the vehicles includes an internal combustion engine and an automatic transmission, the selection of a low gear for producing the braking effect to supplement the parking brake cannot be produced because of the torque converter that is present in the automatic transmission. Therefore, automatic transmissions use separate parking locks instead of a selected gear. The parking lock may, for example, comprise a mechanical interlock in the transmission output shaft on the transmission housing. A ratchet wheel may be provided for this purpose, which is provided with teeth and is arranged on the transmission output shaft such that it rotates with that shaft. Furthermore, a toothed catch is arranged on the transmission housing so that it latches in the spaces between the teeth of the ratchet wheel. When the parking lock is operated and when the vehicle speed is appropriately low, the toothed catch latches suddenly in the ratchet wheel, thereby suddenly stopping the rotary movement of the transmission output shaft. The loads which occur as the catch latches in can generally be damped by the elasticity that exists in the drive train, for example by means of appropriate joints, jointed shafts, suspension, tire damping or the like.
No separate parking lock has yet been provided for vehicles with an electrical drive. Nevertheless, for the same reasons mentioned above, the additional parking lock is also desirable for these vehicles. In fact, electrical drives are subject to different problems relating to the possible use of parking locks, in particular when, as described above, the aim is to use parking locks with a ratchet wheel and a toothed catch.
The electrical drive of a vehicle normally has an electrical machine comprising a rotor, a stator and power electronics for controlling the electrical machine. The torque produced by the rotation of the rotor is in this case used as the basis of the drive for the vehicle. If a parking lock comprising the toothed catch and ratchet wheel as described above were to be used, the rotor rotation would have to be braked via the ratchet wheel and the toothed catch. When the toothed catch suddenly latches in the ratchet wheel, the rotor is suddenly brought to rest. Due to the high torques and the rotor inertia, very high forces are produced by the sudden stop in rotation which are not damped as easily as in the configuration having an internal combustion engine and automatic transmission.
Accordingly, conventional commercially available parking locks can not be used since they would not be adequate for withstanding the occurring loads and would be damaged very quickly. To overcome this problem, parking locks of considerably greater size would have to be used or damping elements would have to be integrated into the parking locks. However, both of these solutions necessitate a large installation volume and would have a very high intrinsic weight, which is a major disadvantage, particularly in automobile construction. Furthermore, parking locks of such a design are considerably more expensive. Furthermore, the development of appropriately modified parking locks for the electrical drive of a vehicle would involve a major time penalty and design effort.
Since the high torque peaks and reductions to be compensated for occur only during the latching-in process, and thus only very briefly, the use of parking locks designed for these maximum loads would not be acceptable financially, for the reasons stated above.
An object of the present invention is to provide a parking lock and an electrical drive for a vehicle, in which the described disadvantages are avoided. More specifically, it is an object of the present invention to provide a parking lock for use with an electric drive that is physically simple and cost-effective.
According to an embodiment of the invention, the object is achieved by a parking lock for a vehicle having an electrical drive train, wherein the electrical drive train includes an electrical machine with a rotor, a stator having a number of stator windings, and power electronics for controlling the electrical machine, the parking lock having a mechanical component which is mechanically operatively connectable to the electrical drive train when the parking lock is operated to stop rotary movement of the electric drive train.
According to the present invention, this parking lock is distinguished in that it has both a mechanical component and an electrical component. The mechanical component may be mechanically operatively connected to the electrical drive train when the parking lock is operated to stop the rotary movement of the electric drive train. Examples of this will be described in more detail further on in the description. The electrical component is designed for producing a short-circuit in the stator windings, at least temporarily, when it is intended to operate the parking lock. The present invention also provides for the electrical component to be activated in a specific time interval before operation of the mechanical component when the parking lock is operated.
The parking lock according to the invention also allows vehicles having an electrical drive to be provided with a simple and cost-effective with a braking system which protects the vehicle from rolling away inadvertentlyxe2x80x94preferably in addition to a conventional parking brake.
The fundamental idea of the parking lock according to the invention is that the characteristic properties of the electrical machine are incorporated in the parking lock. To this end, the parking lock has an electrical component in addition to the mechanical component. The electrical component is designed so that it can, at least temporarily, switch the stator windings of the stator to be active so that the individual windings of the electrical machine are connected to one another, as a result of which a short-circuit is produced in the stator windings. The short-circuit produces a high braking torque in the electrical machine. This braking torque brakes the rotary movement of the electrical drive train.
The mechanical component of the parking lock is not activated until a specific time interval has elapsed, which allows the rotary movement of the electrical drive train finally to be brought to rest in this case. Since, owing to the short-circuit, the rotary movement of the electrical drive train has already been braked by the previous braking process, high torque peaks on the mechanical component of the parking lock are avoided. This allows even relatively small parking locks to be used.
If, for example, parking locks having a ratchet wheel and toothed catch are used, parking locks of relatively small size may be used, such as those which are already used in vehicles with an automatic transmission of the same order or magnitude. These parking locks are already produced in large quantities, so that they are very cost-effective. Furthermore, such parking locks may also be produced easily.
The activation of the electrical component prior to the activation of the mechanical component thus eliminates the need for relatively large parking locks or for any additional components such as damping elements or the like to compensate for the high torque peaks that occur.
The time interval between activation of the electrical component and of the mechanical component is advantageously between 10 and 100 milliseconds. The driver of the vehicle does not notice such short time intervals. Accordingly, the prior temporary production of a short-circuit via the activation of the electrical component, which will be explained in more detail further on in the description, is not perceptible in the form of any discomfort by the driver. Nevertheless, these time intervals are long enough to initiate the braking of the rotary movement of the electrical drive train even before the activation of the mechanical component. The suitable time interval may be set as required, depending on the application. Time intervals other than those described here are also, of course, conceivable.
An example of a suitable mechanical component of the parking lock will now be described in the following text. This parking lock preferably has a toothed ratchet wheel and a toothed catch. These mechanical component correspond to a parking lock as is already used in automatic transmissions, in the manner described above. However, other types of mechanical components are also conceivable, so that the invention is not limited to the exemplary embodiment described explicitly in the following text. Any mechanical interlock for releasably holding the rotor stationary relative to the stator may be used.
The ratchet wheel is provided with teeth and may, for example, be connected to a shaft of the electrical drive train such that the ratchet wheel and shaft rotate together. The toothed catch may be attached to an appropriate housing of the electrical drive train. Upon operation of the mechanical component, the toothed catch is inserted into the ratchet wheel, thereby abruptly stopping the rotation of the ratchet wheel. However, the torque peaks which occur in this case have already been dissipated by the prior braking of the rotary movement of the electrical drive train via the electrical component.
The use of a ratchet wheel and a toothed catch as the mechanical component of the parking lock offers a number of advantages. For example, it is possible to reliably protect the vehicle against rolling away forward or backward even on a steep grade and even if any additional parking brake which may be provided is released. Furthermore, the ratchet wheel and the toothed catch can be configured appropriately to ensure that, once the interlock is latched in, it can also be released again without any difficulties, even on a steep grade.
Operation of a parking lock normally requires that the parking lock is intended to latch in reliably up to a certain speed, such as, for example less than or equal to 5 km/h. Furthermore, it is also intended to be impossible for it to latch in above a specific speed such as, for example, at speeds of 8 km/h or more. This prevents the driver from inadvertently activating the parking lock while driving. These requirements can be satisfied by using a ratchet wheel and a toothed catch. Appropriate design of the teeth and of the spaces between the teeth ensures that the ratchet teeth are thrown out of the way by the inclines on the teeth of the ratchet wheel, so that interlocking is impossible above, for example, the speed of 8 km/h or more. This process of throwing the teeth out of the way is normally audible as noise. Since already existing ratchet wheel systems may be used, the risk of inadvertent interlocking may be prevented since these systems have already been very well proven in practice.
Advantageously, the mechanical component is or can be mechanically operatively connected to the electrical drive train via an electrical or mechanical operating device when the parking lock is operated. The electrical operating device may, for example, comprise an electric motor which causes the toothed catch to engage with the ratchet wheel. However, the toothed catch may also be operated via an appropriate cable run. Other possible operative connections are, of course, also conceivable, so that the invention is not limited to the described examples.
The electrical component may advantageously have a control device via which a short-circuit is or may be produced in the stator windings. This control device is used to produce signals which are then transmitted to a component of the electrical machine such as, for example, power electronics connected to the stator. The stator windings are connected for normal operation via appropriate converters and power semiconductors located within the power electronics. The signal transmitted by the control device ensures that the interconnection of the individual stator windings is briefly changed so that they are connected to form a short-circuit.
The electrical component preferably has at least one sensor element connected to the control device. In this case, the at least one sensor element is advantageously designed to produce signals using which a short-circuit is or can be produced in the stator windings. Any system data required for activation of the electrical component can be detected, and passed on to the control device, via the at least one sensor element.
One of the sensor elements may comprise a position sensor. The position sensor is advantageous, for example, when the operation of the parking lock is initiated via a control element such as, for example, a control lever. Such an example will be explained in more detail further on in the description. When the control element is moved to a position which is intended for activation of the parking lock, this operation of the control element is detected via the position sensor. The detected data are passed on to the control device where they are further processed. The control device then produces a signal which causes the stator windings to be short-circuited.
Furthermore, the at least one sensor element may comprise a speed sensor. This sensor measures the present speed of the vehicle and passes this measurement on to the control device. The limiting value for a maximum speed may, for example, be stored in the control device, wherein the maximum speed is the speed above which the parking lock must be prevented from being activated. If the measured speed is below this maximum value, the electrical component of the parking lock may be activated. The control device will emit an appropriate signal to short-circuit the stator windings.
If the measured present speed value is above a maximum permissible limiting value, it is impossible to activate the electrical component of the parking lock, so that the stator windings are not short-circuited.
In both cases, the mechanical component may be activated independently of the activation of the electrical component. In this case, the mechanical component is activated after the specific time interval. If the present speed of the vehicle is above the limiting speed for activation of the parking lock this will, however, not lead to any problems since the mechanical component will not latch in at the higher speed. If a ratchet wheel and a toothed catch are used, the teeth of the toothed catch will be thrown away from the ratchet wheel above a specific speed as described above.
According to the second aspect of the present invention, an electrical drive is provided for a vehicle which has a drive train for driving vehicle wheels, in which case the drive train has an electrical machine with a rotor, a stator having a number of stator windings, and power electronics for controlling the electrical machine, and has a transmission. According to the invention, this electrical drive is distinguished by the provision of a parking lock according to the invention, as described above.
In the case of such an electrical drive, a parking lock can be provided using simple means and in a cost-effective manner and can be used, for example, as a second braking system in addition to a parking brake. With regard to the advantages, effects, influences and method of operation of the drive according to the invention, reference is made to the entire contents of the above statements relating to the parking lock according to the invention.
The electrical drive comprises an electrical machine for producing the required drive torque. The invention is not limited to specific machine types. However, synchronous machines and, in this case, in particular synchronous machines with permanent-magnet excitation, are advantageously used. The speed reduction or increase is carried out in the downstream transmission. The transmission may also be followed by a differential, which then transmits the drive torque to the vehicle wheels.
The mechanical component of the parking lock may advantageously be arranged rim between the electrical machine and the transmission. This is an installation point at which high speeds and relatively low torques occur. The mechanical component may comprise a ratchet wheel design which may be connected to the rotor shaft such that the shaft and ratchet wheel rotate together. The toothed catch may then be connected to the housing of the electrical machine. In another embodiment, the mechanical component of the parking lock may be arranged between the transmission and the differential. This is an installation point at which relatively low speeds and relatively high torques occur. If a ratchet wheel design is used, the ratchet wheel can be connected to the differential cage such that they rotate together. The toothed catch may then be connected to the differential housing. Both embodiments require only a very small physical space.
The transmission may comprise an epicyclic transmission arranged coaxially with respect to the rotor shaft. Epicyclic transmissions generally have a sun wheel, a hollow wheel and various planet wheels which are arranged on a satellite carrier, with the individual wheels being arranged and aligned coaxially with respect to one another. In this way, an epicyclic transmission represents a highly effective transmission with only a small space requirement.
The mechanical component of the parking lock and the transmission may advantageously be arranged within the electrical machine. Electrical machines comprising an external rotor normally include free space at its center. Accordingly, a large portion of the transmission and the mechanical components of the parking lock may be integrated within the electrical machine. This allows particularly short physical axial lengths to be achieved.
In a further refinement, a control element such as a control lever guided in a gearshift console may be provided to operate the transmission and to operate the parking lock. In this case, the parking lock may be activated either electrically or mechanically. If the activation is electrical, stator windings are first of all short-circuited. After a short timer interval, the mechanical component is then actuated electrically. If the activation is mechanical, a switch or the like is advantageously integrated in the control element and generates a signal before the parking lock latches in mechanically, the sitch activates the short-circuiting of the stator windings.
The sensor element which is in the form of a position sensor may advantageously be connected to the control element. In this way, the movement of the control element to the appropriate park gearshift position is detected by the position sensor and the signal is then transmitted to the control device. The stator windings are short-circuited via this control device. Once the control element has reached the desired park gearshift position, the mechanical component is activated. The time delay between the production of the signal by the position sensor and the activation of the mechanical component, which corresponds to the defined time interval, is sufficient for the rotor to be braked by the short-circuit produced in the stator windings such that the mechanical connection can now be produced between the mechanical component and the rotor without overloading the mechanical parts.
The control device for the parking lock is preferably connected to the power electronics of the electrical machine.
In a further refinement, an additional parking brake can also be provided for the vehicle wheels, so that the vehicle has two braking systems, overall.
Finally, according to the third aspect of the invention, a method is provided for operating a parking lock according to the present invention for a vehicle having an electrical drive, and which is distinguished according to the present invention by the following steps: a) activating the electrical component of the parking lock for producing a short-circuit at least temporarily in the stator windings of the stator; b) activating the mechanical component of the parking lock after a specific time interval has elapsed after step a) for connecting the mechanical component to the electrical drive train and prevent rotary movement of the electric drive train.
The method according to the present invention allows the use of a parking lock even for a vehicle with an electrical drive in a simple and cost-effective manner, in which case an already known device may be used as the mechanical component of the parking lock. The mechanical component may be designed to be relatively small in comparison with the maximum possible torque peaks. The advantages, influences, effects and method of operation of the method according to the invention are described above with reference to the discussion of the parking lock according to the present invention and the electrical drive according to the present invention.
The mechanical component of the present invention may advantageously be activated 10 to 100 milliseconds after the activation of the electrical component.
The electrical component of the parking lock is preferably activated only below a specific vehicle speed, which is preferably less than or equal to 5 km/h. As has already been stated above, this prevents the stator windings from being inadvertently short-circuited above a speed at which such activation of the electrical component could be dangerous.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.